Cathode ray apparatus



June 25, 1935. A, w. VANCE CATHODE RAY APPARATUS Filed Oct. 15, 1952luv/ me: ArZhm'I IZ Ham's.

mw tg HIS A TT'OIEWEK Patented June 1935 UNITED STATES CATHODE RAYAPPARATUS Arthur W. Vance, Camden, N.. 1., minor to Radio Corporation ofAmerica, New York, N. Y., a corporation of Delaware Application October15, 1932, Serial No. 637,885

3- Claims.

' tube at the transmitting station, and in which the tube comprises aphotosensitive mosaic screen on which an image of an object isprojected, and

which is scanned by a cathode ray, it has been found to be advantageousto project the image on the same side of the screen which is scanned bythe ray. When this is done, the axis of the optical system forprojecting the image is preferably perpendicular to the screen, but theaxis of the so-called gun for developing and directing the ray ofelectrons is, of necessity, disposed at an acute angle to the screen. Onaccount of this arrangement, the outline of the area scanned by the rayhas a keystone shape rather than the desired rectangular shape. Thisdistortion of the scanned pattern is manifested by a substantial and.corresponding distortion of the reproduced image at the receivingstation, the reproduced image being also the shape of a keystone, withthe vertical lines inclined to each other.

With the foregoing in mind, it is one of the objects of my invention toprovide an improved television system of the character referred towherein the keystone distortion is corrected.

Other objects and advantages will hereinafter appear.

In accordance with my invention, in a cathode ray tube of the characterreferred to, the ray is deflected in part by an electromagnetic fieldwherein the flux is disposed in planes substantially perpendicular tothe axis of the electron gun, and wherein the distribution of the fluxdensity on one side of the axis of the gun is dif-- ferent than suchdistribution on the other side of the axis. In this manner, the ray iscaused to scan a keystone area in an intermediate plane perpendicular tothe axis of the electron gun, whereby the ray is caused to scan thesurface of the inclined screen structure over a substantiallyrectangular area.

. ratus of the character hereinafter described and claimed.

For the purpose of illustrating my invention, an embodiment thereof isshown in the drawing, wherein Figure 1 is a perspective'view, partlydiagrammatic, of a television transmitting app ratus embodying myinvention;

Fig. 2 is a simplified, sectional view, the section being taken on the'line 2-2 in Fig. l; and 5 Fig. 3 is a diagrammatic view illustrative ofthe principle of operation.

With reference to Fig. l, the reference numeral i0 designates a cathoderay tube provided with some suitable form of mosaic, photosensitivescreen structure 82 upon which an image of the object is projected. Thescreen structure 62 comprises, generally, a supporting plate provided onthe front surface thereof with a great number of minute metallicelements insulated from each other and from the plate, and each providedwith a coating of photosensitive material.

An image of the object, shown as being in the form of a moving picturefilm i i, is projected upon the photosensitive surface by a suitableoptical system it, the axis it of which is perpendicular to the screenstructure i2.

An electron gun 20, of any suitable construction, operates to develop amy 22 of electrons, and to direct the ray at the photosensitive surfaceof the screen i2, the axis 24 of the tube being inclined at an acuteangle of about 60 to the plane of the screen I 2.

For the purpose of causing the ray 22 to scan the photosensitive surfaceof the screen i2, sawtooth current waves at different frequencies arecaused to flow through the coils 26, 28, 30 and 32. The coils 26 and 30operate to deflect the ray vertically, while the coils 28 and 32 operateto deflect the ray horizontally.

In the constructions proposed heretofore, the ray 22 scanned the screeni2 over a keystone area ABCD as shown in Fig. 3, and as furtherillustrated in Fig. 1. This is accounted for by the fact that the screeni 2, in these constructions, was disposed at an acute angle to the axis24 of the electron gun.

For the purpose of correcting for this action, I propose to make thecoil 32 of a substantially greater number of turns than the coil 28, sothat the deflecting field below the center line 34 of the tube will besubstantially stronger than the field above this line. 'By thisarrangement, the tendency is for the ray 22 to scan a keystone area EFGHin a planeperpendicular to the axis 24 of the gun. Therefore, when theray strikes the screen l2; it will scan the surface thereof over asubstantially rectangular area JKLM.

In cathode ray tubes of this type constructed so 6 hen. That is, thereisuneven spacing betw the horizontal lines, the spaces between adjacentlines increasing from the lower edge of the scanned area to the top edgethereof. In my improved apparatus, 1 correct for this distortion bycausing the vertical deflecting field to inc es the seem is deflectedvertically, toward the portion of the screen where the lines are crowdedand this is done by supporting the vertical defleeting cells 26 and 39with the center line 3% oi the poles thereof ofiset or spaced downwardlyfrom the center line 36 oi the tube 98.

It be understood that various m tions within the conception of thoseskilled in the art are possible without departing from the spirit of myinvention or the scope of the c.

I claim as my invention:

1. Cathode ray epperatus comprising screen structure, means fordeveloping a ray oi electrons and directing the ray at one side oi saidstructure, and means for deflecting said my to cause the same to scanseid structure, said deflecting means compriidng coils csed tively onopposite sides of the axis oi sold roydeveloping means, the turns of onecoil bemg substantially greater in number than the t of the other cell.

2. Cathode my cpperretue comp screen structure, menus for developing omy of electrons end ectine the my act one-side oi emd structure, theaxis of said ray-developing means being inclined at an acute angle tosaid structure, and means for deflecting the my to cause the some toscan it keystone area, in a. plane perpendicular to said axis wherebythe ray is caused to the surface of said structure over a. substontieilyrectangular area, said ray-deflecting meens comprising coils disposedrespectively on opposite sides of the axis of said ray-developing meter,the. of one coil being substantially greeter in number then the turns ofthe other coil.

3. Cethode rey apparatus comprising screen structure, means iordeveloping a. ray of electrons and directing the ray at one side of saidstructure,- the axis of said ray-developing means being inclined at anacute angle to said structhe same to seen the surface of said structure;sold deflecting means comprising a. first set of complementarydeflecting devices disposed respectively on opposite sides of said axis,the

center line of sold devices being substantially the second set beingsubstantially greater in number then the turns of the other coil of thesecond set. I

An W. VANCE.

,ture, and means for deflecting the my to cause

